Minor losses are pressure drops occurring at fittings, valves, bends, and other pipe components, expressed as a fraction of dynamic pressure and calculated separately from friction loss in straight pipe. These losses become significant in systems with numerous fittings and can equal or exceed straight-pipe friction losses.
Calculation Methods
Minor losses use loss coefficients (K-values) multiplied by velocity head, expressed as psi. A 90-degree elbow typically has K-value of 0.9, a tee-fitting 1.0, and a ball valve 0.05. Summing all K-values and multiplying by velocity head gives total minor losses. Equivalent length method simplifies this by converting K-values to pipe lengths.
System Impact
In systems with short runs and many fittings, minor losses can represent 50% of total pressure drop. Careful component selection, such as long-radius elbows over standard elbows, reduces K-values by 30-40%. Balancing valves, strainers, and check valves contribute significant losses requiring careful sizing during design to prevent excessive pump head demands.